1. Field of the Invention
The present invention relates to global position systems, GPS, and more particularly to an improvement for detecting and excluding erroneous information from a transmitting satellite in order to assure greater accuracy and integrity.
2. Description of the Prior Art
U.S. Pat. No. 5,760,737 (herein xe2x80x9cthe ""737 patentxe2x80x9d) entitled xe2x80x9cNavigation System with Solution Separation Apparatus for Detecting Accuracy Failuresxe2x80x9d issued Jun. 3, 1998 to Mats Brenner, and assigned to the applicant of the present invention, discloses a GPS system for determining when an error occurs in one of a plurality of transmitting satellites, and for establishing an accuracy or xe2x80x9cerror boundxe2x80x9d. This is achieved using a position solution obtained from at least five transmitting satellites and comparing that with a plurality of position sub-solutions, each of which is derived from a different subset of the at least five transmitting satellites. Specifically, a filter that excludes a different one of the transmitting satellites is employed to obtain the sub-solutions. This yields a plurality of solution separation parameters each based on the statistics of a separation between the position solution and respective position sub-solution. A plurality of discriminators, each based on the distance between a position solution and a respective sub-solution, is obtained and an indicator indicates a fault when one of the discriminators is greater than one of the solution separation parameters.
Unfortunately, the determination that a fault exists does not provide information as to which of the transmitting satellites is in error.
The present invention employs a plurality of sub-sub solutions for each of the sub-solutions. Each sub-sub-solution excludes a different satellite in addition to the satellite excluded by the parent sub-solution. As was the case with the parent solution, the separation between each sub-sub-solution and its parent sub-solution is compared to a detection threshold. If the separation for a particular sub-solution and any of its sub-sub-solutions exceeds the detection threshold then the satellite represented by the particular sub-solution cannot be the failed satellite. If one and only one sub-solution is found for which the separation between it and all of its sub-sub-solutions are less than the detection threshold, that the satellite represented by that sub-solution is the failed satellite.